why Fy = 0 when i give a point load on foundation

Hello Rachata,
FY is the resulting reaction on the nodes when a prescribed displacement is applied.
You may refer to an article (introduction) in the link here to know when a force load is used, how much a load step is applied per step via SMstage: communities.bentley.com/.../how-to-get-a-load---displacement-curve-using-scripting-interface

Thank you Hung

Can I ask more question? If in the field I start give load at 2kN/m2 and add 2kN/m2 every hour until reach 20kN/m2. 

what should i set up in staged construction 

Hello again, Rachata,
You may define multiple phases with an increment of the load in each phase = 2 kN/m2, e.g., Phase_1: 2 kN/m2, Phase_2: 4 kN/m2, etc. 

Hello again, Rachata,
You may define multiple phases with an increment of the load in each phase = 2 kN/m2, e.g., Phase_1: 2 kN/m2, Phase_2: 4 kN/m2, etc.